Prostate cancer (PCa) is the second leading cause of cancer-related deaths in American men. Current treatment modalities for metastatic disease and androgen refractory prostate cancer are mostly palliative with poor prognosis. Early diagnosis and prevention are critical to limit the impact of this disease. Epidemiogical studies indicated that patients receiving diabetic drug metformin have lower prostate cancer risk and better prognosis and suggested that the metformin may have anti-neoplastic effects. This study is to elucidate the mechanism by which metformin impede prostate cancer initiation and progression. MYC oncogene is frequently amplified in prostate cancer and its amplification involves in early prostate epithelia cell transformation and the onset of prostate cancer. MYC amplification not only contributes to early transformation of prostate epithelial cells, but also alters prostate tumor sensitivity to mammalian target of rapamycin (mTOR) inhibitors. Our preliminary data demonstrated that metformin reduces the MYC oncogene levels both in vitro and in vivo. Our central hypothesis is that metformin acts as a chemoprevention agent to restrict the initiation of prostatic intraepithelial neoplasia (PIN) and the growth of cancer associated wit down-regulation of MYC. Aim 1. To examine the inhibitory effect of metformin on prostate cancer initiation and MYC expression in vivo. The working hypothesis is that the metformin alleviates PIN and works synergistically with mTOR inhibitor in Hi-Myc mice. Male Hi-Myc mice will be treated with metformin, metformin plus rapamycin or vehicle for 12- and 24-weeks and MYC, testosterone (T), dihydrotestosterone (DHT), androgen receptor levels, proliferation, apoptosis indices and microvessel density will be determined. Number of PIN and PCa lesions will be enumerated and correlated to MYC levels. Aim 2. To define the epigenetic responses to metformin in prostate. The working hypothesis is that the metformin reduces MYC associated with epigenetic alterations. We will explore metformin influences on epigenetic alterations in mouse prostates by isolating RNA from early time-point of detectable reduction of MYC protein levels in prostate glands from metformin treated Hi-Myc mice and human primary prostate epithelial cells using Epigenetic Chromatin Modification Enzymes PCR Array. Quantitative RT-PCR and western blots will be used to validate the epigenetic enzymes regulated by metformin. Prostate tissue microarray slides including normal, PIN and PCa tissues will be applied do determine the correlation among these epigenetic enzyme expression levels to PCa progression. This proposed study is the first preclinical study to evaluate metformin as a chemopreventive agent in treating prostate neoplasia and cancer at early stage (i.e. those with PIN or high-grade PIN). The novel combined cancer prevention therapy using metformin and mTOR inhibitors proposed in this study may display promising synergistic efficacy and will be translational to clinical application.